The present invention concerns emissions test apparatus, and more particularly concerns an apparatus adapted to pressure test a vehicle fuel holding system including related components for vapor emitting leaks leading to hydrocarbon emissions in the form of evaporated fuel.
Fuel tank assemblies of vehicles in service periodically experience warming, causing the atmosphere in the vehicle fuel holding system to expand. If left uncontrolled, the expanding atmosphere discharges a considerable amount of environmentally harmful hydrocarbon vapors (i.e. gasoline or fuel vapors) into the environment. In an effort to control the discharge of these hydrocarbon vapors, modern vehicles now include fuel caps that sealingly close a fill tube access port to the vehicle fuel tank assembly. Further, the modern vehicles have an evaporative emissions control system which feeds vapors from the fuel tank assembly to the vehicle engine for burning or which otherwise contains the vapors or treats the vapors to reduce their harmful qualities before the vapors are released to the atmosphere.
These systems are generally effective; however, it is desirable to test the integrity of the fuel tank assembly and evaporative emissions control system to assure that there are not any leaks that would allow vapors to bypass the system and be discharged into the environment. Further, government regulations may soon require testing of vehicles that have been in service for a period of time, since such undesirable leaks can develop or worsen during the service life of a vehicle. Unfortunately, the leaks, if present, typically occur at component joints under the vehicle where they are most difficult to find or see, especially if the vehicle has been in service and has a dirty underbody. Still further, the leaks most commonly occur above the fuel level such as on the top side of the fuel tank where the evaporative emissions control system or fuel delivery system attaches to the tank, which top side is hidden from view and difficult or impossible to inspect even on a vehicle hoist.
In response to the above, at least one domestic automotive company has proposed an "all manual" evaporative emissions test method for vehicles which would include providing a special test port attached to the existing evaporative emissions control system or, alternatively, include providing a special test port in a specially adapted "replacement" fuel cap used only during testing. An "all manual" emissions tester would be connected to the special test port, and a pressure source such as an air compressor would be connected to the tester to pressurize the atmosphere of the vehicle fuel tank assembly and the evaporative emissions control system. The "all manual" proposed emissions tester would further include a pressure regulator to control the pressurization of the atmosphere, a shutoff valve to prevent back-flow of the pressurized atmosphere, a pressure gauge for sensing the pressure of the atmosphere over time, and a flexible hose with a connector for connecting to the special test port. The "all manual" proposed test would be controlled manually, with an operator controlling the initial pressurization and stabilization of the atmosphere, and then manually determining the change in pressure over a predetermined time period.
However, the "all manual" proposed tester and test method would not be entirely satisfactory since the manual control over the test and tester could potentially lead to inaccurate and misleading results. This is because manually operated tests depend to a large degree on the precision, accuracy and attention of the operator running the test. Further, particularly in vehicles that are borderline in regard to passing or failing the test, the operator may be biased to misread the tester so that the operator receives additional work (even though the repair is not required) or, alternatively, so that the operator does not need to do any work (even though the repair should be done), depending upon the preference of the operator. Still further, it is undesirable to require special test ports on the vehicle since this adds to the cost of the vehicle without giving any visible benefit to the consumer. Additionally, it is desirable to test the vehicle fuel holding system as a complete unit rather than individual components one at a time, and thus it is frequently undesirable to remove the existing fuel cap from the vehicle during testing.
Prior art also includes at least two types of other "all manual" testers for testing for fuel leaks in fuel tank assemblies, as disclosed in the disclosure statements submitted with this application. However, these two types of testers are manually operated, and thus depend on the precision, accuracy, and attention of the operator, which results in the problems discussed above. Also, these two testers are for pressure-testing a fuel tank assembly, and not for testing an entire fuel system including an evaporative emissions control system connected to the fuel tank assembly.
It is desirable that any test apparatus for testing for gas vapor leaks be portable and adapted for use in a wide range of circumstances, such as in service stations having different levels of sophistication and expertise. However, as test apparatus are made more sensitive, their reliability and accuracy does not necessarily improve. For example, test apparatus of the type disclosed in this application requires a source of clean pressurized gas. However, many sources of compressed gas are relatively unclean, such as compressed air from air compressors at many service stations. Unclean compressed gas can quickly foul and destroy the accuracy and reliability of a test apparatus for testing leaks. Bottled compressed gas is usually relatively clean, however the bottles of compressed gas tend to provide an unstable, uncertain gas pressure, particularly as the bottle runs low and the internal pressure of compressed gas in the bottle drops off. This adversely affects the accuracy and reliability of the test apparatus. Regulators can be used on the bottles of compressed gas in an effort to provide a continuous gas pressure and continuous stable flow of gas from the bottles of compressed gas, however the gas pressure is only roughly controlled and is not as well controlled as desired. Further, the regulators are reactive, such that the gas flow experiences surges and non-uniform flow as a shut-off valve on the bottles of compressed gas are opened. This can adversely affect the accuracy of the test apparatus and further can damage highly sensitive sensors in the test apparatus. Additionally, the surge control and the pressure control must be accomplished at relatively low gas pressures and with relatively inexpensive components so that the emissions test apparatus can be purchased by local service stations at remote and rural locations without large capital expenditures.
Thus, a test apparatus which is accurate and which operates substantially independent of an operator during the actual test sequence is desired. Further, a test apparatus is desired which minimizes the overall cost of any test apparatus and method developed including minimizing any special parts required to be permanently or temporarily assembled to the vehicle.